The present invention relates to balloon catheters and, more particularly, to an elastomeric balloon configured to expand to a predetermined diameter upon application of a predetermined pressure thereto.
Balloon catheters are well known in the art. Such catheters are employed in a variety of medical procedures, including dilation of narrowed blood vessels, placement of stents and other implants, temporary occluding of blood vessels, etc.
In a typical application, the balloon is advanced to the desired location in the vascular system. The balloon is then pressure-expanded in accordance with a medical procedure. Thereafter, the pressure is removed from the balloon, allowing the balloon to contract and permit removal of the catheter. It is to be appreciated that the balloon must be formed of an elastomeric material which is readily pressure-expanded, yet will also readily contract upon removal of the inflation pressure.
Procedures such as these are generally considered non-invasive, and are often performed in a manner which minimizes disruption to the patient's body. As a result, catheters are often inserted from a location remote from the region to be treated. For example, during angioplasty procedures involving coronary vessels, the balloon catheter is typically inserted into the femoral artery in the groin region of the patient, and then advanced through such vessel into the coronary region of the patient. These catheters typically include some type of radiopaque marker to allow the physician performing the procedure to monitor the progress of the catheter through the body. However, because the balloon portion of the catheter is not visible to the physician, such balloon may be overexpanded during inflation without the physician's awareness.
Attempts have been made in the past to control and limit overexpansion of catheter balloons. One improved balloon is disclosed in U.S. Pat. No. 4,706,670. The balloon of the '670 patent, along with the catheter tubing, is reinforced by continuous helical filaments which repeatedly cross each other. The filaments are formed as a braid which are embedded or otherwise encased in the yielding plastic material. The filaments are arranged such that prior to pressurization of the balloon, the filaments of the balloon portion lie at an angle which is less than a neutral angle of 54.73.degree. relative to the axis of the balloon. As the balloon is inflated, the angle of the filaments in the wall of the balloon approach the mentioned neutral angle. This neutral angle represents the equilibrium point of the balloon at which point the circumferential stresses in the balloon balance the axial stresses in the balloon, such that a further increase in the internal pressure of the catheter will not produce any further increase in the diameter of the balloon.
Under ideal conditions, the balloon would reach its maximum diameter at the point where the reinforcing fibers reach their neutral angle. However, due to limitation in the materials and to interaction between the elastomer and the reinforcing fibers, the actual performance of the balloon will vary. For example, the reinforcing fibers are typically extensible to some degree, allowing the balloon to continue expanding even after the filaments reach their neutral angle. Moreover, the reinforcing fibers employed in the balloon may soften as the balloon is repeatedly inflated and deflated, again allowing the balloon to overexpand upon inflation. The reinforcing fibers and the balloon may also interact in a manner which introduces undesirable torsional moments into the balloon. Finally, the elastomeric properties of the balloon may cause such balloon to "bulge" through the open regions between the reinforcing fibers.
Accordingly, there is a need in the art for a reinforced elastomeric balloon having a predefined maximum expanded diameter. This maximum expanded diameter should remain constant even as the pressure of the balloon is increased. Moreover, this maximum expanded diameter should remain constant upon repeated inflation and deflation of the balloon. The pressure required to reach maximum expansion should be calculatable based on the chosen elastomer and the diameter of the expanded and unexpanded balloon. Finally, the reinforcing structure should be configured to reduce unwanted forces transferred between the reinforcing structure itself and the elastomer during the inflation procedure.